The following description will be directed to the use of the double-plug lock of the invention in hotels and the motels. However, it will become evident as the description proceeds that the lock has general utility, for example, in institutions, industrial plants, government facilities, and so on, where changes in the locks are required with some frequency, and where master keying is employed.
Problems have arisen during recent years in preventing theft from hotel and motel rooms due to the unauthorized use of the key issued to guests and maids. Such keys are often lost, stolen, or otherwise find their way into the hands of thieves. The problem is aggravated because the prior art hotel keys normally carry identifying tags which gives the thief the exact information as to the name of the hotel, its address, and the room number to which access may be gained by use of the particular key.
A principal objective of the present invention is to provide a lock which may be readily reset after each occupancy, so that the previous guest's key no longer fits the lock, and so that the lock may be set to accept a new guest key.
The lock to be described is a double-plug type, so that one key may be issued to each guest and a different key may be issued to the maid, and so that the maid's key and the guest's key may be used to operate the lock independently of each other. Precautions are built into the lock, so as to prevent the guests themselves from resetting the locks, this being achieved by the provision of a program key which must first be inserted into th maid's plug of the lock to turn the maid's plug to a position in which the guest plug is released. Only then may the guest plug be turned to its resettable position.
The mechanism included in the individual plugs may be of the type described, for example, in Copending Application Ser. No. 648,176 filed Jan. 12, 1976 and now U.S. Pat. No. 3,999,413. A feature of the lock described in the copending application is the provision of a simple assembly which may reset at will to receive a different key, without the need for any special tools, and merely by turning the lock by the current key to a resettable position, withdrawing the current key, inserting a new key, and turning the lock back to its normal position by the new key. The lock is thereby set so that it cannot be unlocked by the previous key, but it can be unlocked only by the new key.
The individual plugs of the double-plug lock of the invention, like the lock of the copending application, includes an anti-pack feature in the form of a pick bar which engages the tumblers of the lock whenever the plug is turned from a reference position. The pick bar prevents movement of the tumblers unless the plug is in the reference position. This means that unless the proper key is inserted into the lock, when the plug is in its reference position, initially to move the tumblers to their proper positions so as to permit the plug to be turned from the reference position and unlocked, no unlocking operation is possible. This is because the tumblers are immediately locked in their relative positions as set by the inserted key, upon an initial turning of the plug by the key from the reference position.
Another feature of the lock of the invention is that it can be made simply, economically, and on a mass production basis. This is because each lock can be made exactly the same as all others, and each individual lock need not be designed to accept one particular key. Moreover, the purchaser of the lock of the invention may change it to accept a new key, at any time, and without the need for any extraneous tools. However, this cannot be achieved by the guest himself as will be described. Also, the maid's lock cannot be changed, except by a person having access to the program key. Also, as described, the lock of the invention has an advantage in that it can be constructed to have approximately the same size as the prior art mortise cylindrical locks, so that it can easily be mounted into existing door hardware to replace existing cylindrical locks, without the need for costly retrofit operations.